1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a method for operating a data communication service in a global system for mobile communication (GSM).
2. Description of the Related Art
In general, GSM is a digital system for operating limited frequency resources using time division multiple access (TDMA), enabling a plurality of mobile subscribers or user equipments (UE) to simultaneously communicate via a corresponding channel. The GSM is the standard used in mobile communication systems in Europe.
Because all countries in Europe adopt the GSM, the subscribers can use the same UE in any country and receive mobile communication services through their UE according to a roaming service. In addition, the subscribers can be directly provided with a voice communication service by carrying subscriber identity modules (SIM) to record their personal information such as international mobile subscriber identity (IMSI). As such, a subscriber can rent or use a UE in any country in Europe by connecting his SIM to the UE.
A data communication service provided by the GSM in Europe is called a general packet radio service (GPRS). The GPRS is provided only in home areas that are service areas of a mobile communication system where the UE has been registered. That is, the GPRS is not provided in roaming areas where the UE has not been registered. The GSM and the GPRS have been disclosed in the U.S. Pat. Nos. 6,208,628 and 6,480,717. The home areas are service areas of a first mobile switching center (MSC) where the UE has been registered, and the roaming areas are service areas of a second MSC (GSM) where the UE has not been registered.
When the user attempts voice communication in a roaming area by using the GSM type UE, the user can use the voice communication according to the roaming service. However, a second MSC may not provide data communication service for GPRS. Accordingly, the MSC transmits a reject signal for rejecting the GPRS request to the UE. UE records and stores the reject signal in a memory area, so that the user cannot use the GPRS even in the home area. For example, when a UE that has recorded a reject signal (for example, ‘GPRS service not allowed’) requests GPRS in the home area, the first MSC in the home area rejects the GPRS request of the UE on the basis of the reject signal recorded in the UE.
In order for the UE recording the reject signal to use the GPRS in the home area, the reject signal must be deleted. For example, the user must delete the reject signal recorded in the memory of the UE with the help of a professional staff, or by temporarily turning off and on the UE. Accordingly, the conventional method for operating the data communication service in the GSM causes inconveniences to the users, and reduces reliability of the GSM.